1.Field of the Invention
The present invention relates to a process of mounting elements and an optical transmission apparatus having elements mounted using this method, for example, an optical interconnection apparatus performing optical interconnection between stacked IC chips employed by a one-chip computer or the like.
2. Description of the Related Art
In order to further improve the operation speed of computers, a one-chip computer has been proposed, which comprises stacked IC chips (e.g., CPU, DRAM, and the like) between which data is transmitted and received using optical signals. Typically, in an optical interconnection apparatus employed by such a one-chip computer, each IC chip is stacked in a manner such that one IC chip (e.g., light emitting element) and another IC chip (e.g., light receiving element) face each other. According to this example, light emitted from an IC chip (i.e., the light emitting element) can be directly received by another IC chip. Accordingly, high-speed data transmission can be realized by transmitting data with such light. Furthermore, if a plurality of IC chips, each having a light receiving element, are stacked, then an optical signal transmitted from a light emitting element can be received by a plurality of light receiving elements. That is, data from a single IC chip can be simultaneously transmitted to a plurality of IC chips, thereby realizing a very high-speed optical bus.
In order to perform parallel data transmission between chips, each signal path must be independent. However, the IC chips are very small; thus, optical signals may leak from the relevant paths, thereby generating so-called crosstalk. It is very difficult and impractical to form an optical waveguide between stacked IC chips so as to solve this problem. Therefore, in order to perform parallel data transmission between chips, it is effective to assign a different signal form, that is, a different wavelength, to each optical signal path.
Here, light emitting diodes, surface emitting lasers, and the like, as light emitting elements, and photodiodes as light receiving elements, are each formed on a semiconductor substrate. It is impossible to assign different optical characteristics, in particular, to form elements having different optical characteristics on a specific portion on the same substrate. Therefore, each light emitting or receiving element must be directly mounted on an IC chip.
A vertical cavity surface emitting laser having a small aperture for light emission is an example of the light emitting element mounted on an IC chip. The size of such a surface emitting laser is sufficiently small as a light emitting element mounted on an IC chip, and this surface emitting laser emits light in a vertical direction. Therefore, if the surface emitting laser can be mounted on the substrate of the IC chip, then the surface emitting laser can immediately emit light to another IC chip mounted in a stacked form. In addition, photodiodes are also sufficiently small as light receiving elements mounted on an IC chip.
However, it is difficult to mount such small light emitting or receiving elements on the base of an IC chip in a highly-integrated structure. Additionally, in order to form an optical bus between stacked IC chips, relevant light emitting and receiving elements must be precisely mounted at each predetermined position on the IC chip. However, it is very difficult to precisely mount these elements in a highly-integrated structure as described above.
In order to solve the above problems, an object of the present invention is to provide a process of mounting elements and an optical transmission apparatus having elements mounted by this method, which can be applied to an optical interconnection apparatus for optical interconnection between stacked IC chips or the like.
Therefore, a process of mounting elements according to a first aspect of the present invention comprises the steps of:
forming concave portions having different forms at predetermined positions on a surface of a base;
forming microstructures on which elements having different functions are provided and which have different forms identical to the forms of the concave portions;
creating a slurry by putting the microstructures, on which the elements are provided, into a fluid; and
fitting the microstructures into the concave portions having the identical forms by making the slurry flow on the surface of the base.
In a process of mounting elements according to a second aspect related to the first aspect of the present invention, slurries, which respectively include the microstructures in order of size from largest to smallest, are made to flow in turn on the surface of the base.
An optical transmission apparatus according to a third aspect of the present invention comprises elements mounted by using a process according to the first or second aspect, wherein the elements which have different functions and are mounted at said predetermined positions on the surface of the base are light emitting elements, each of which emits light of a different wavelength.
An optical transmission apparatus according to a fourth aspect of the present invention comprises elements mounted by using a process according to the first or second aspect, wherein the elements which have different functions and are mounted at said predetermined positions on the surface of the base are light receiving elements, each of which receives light of a different wavelength.
In an optical transmission apparatus according to a fifth aspect related to the fourth aspect of the present invention, the light receiving elements are photodiodes, each having a light receiving surface on which a band-pass filter is provided.
In an optical transmission apparatus according to a sixth aspect of the present invention, the base included in an optical transmission apparatus related to the third aspect and the base included in an optical transmission apparatus related to the fourth aspect are stacked in a manner such that the light emitting elements included in the optical transmission apparatus related to the third aspect respectively face the light receiving elements included in the optical transmission apparatus related to the fourth aspect.
In an optical transmission apparatus according to a seventh aspect of the present invention, the base included in an optical transmission apparatus related to the third aspect and the base included in an optical transmission apparatus related to the fifth aspect are stacked in a manner such that the light emitting elements included in the optical transmission apparatus related to the third aspect respectively face the light receiving elements included in the optical transmission apparatus related to the fifth aspect.
The process of mounting elements according to the first aspect of the present invention comprises the steps of forming concave portions having different forms at predetermined positions on a surface of a base; forming microstructures on which elements having different functions are provided and which have different forms identical to the forms of the concave portions; creating a slurry by putting the microstructures, on which the elements are provided, into a fluid; and fitting the microstructures into the concave portions having the identical forms by making the slurry flow on the surface of the base. Therefore, when the forms of the concave portions agree with the forms of the corresponding microstructures, elements having different functions can be mounted at a very high density. When the forms and positions of the concave portions are precise, the elements can be very precisely mounted on the base.
In the process of mounting elements according to the above second aspect, slurries, which respectively include the microstructures in order of size from largest to smallest, are made to flow in turn on the surface of the base. Therefore, the probability of a small microstructure being placed into a larger concave portion is small, and accordingly, the elements can be more precisely mounted.
The optical transmission apparatus according to the above third aspect comprises elements mounted by using a process according to the first or second aspect, wherein the elements which have different functions and are mounted at said predetermined positions on the surface of the base are light emitting elements, each of which emits light of a different wavelength. Therefore, it is possible to manufacture an IC chip in which the light emitting elements have been mounted; the IC chip can be applied to an optical interconnection apparatus for performing optical interconnection between stacked IC chips.
The optical transmission apparatus according to the above fourth aspect comprises elements mounted by using a process according to the first or second aspect, wherein the elements which have different functions and are mounted at said predetermined positions on the surface of the base are light receiving elements, each of which receives light of a different wavelength. Therefore, it is possible to manufacture an IC chip in which the light receiving elements have been mounted; the IC chip can be applied to an optical interconnection apparatus for optical interconnection between stacked IC chips.
In the optical transmission apparatus according to the above fifth aspect, the light receiving elements are photodiodes, each having a light receiving surface on which a band-pass filter is provided. Therefore, it is possible to easily form the light receiving elements having a filtering function, by which independent signal paths can be formed; such independent signal paths are necessary for performing parallel data transmission of an optical interconnection apparatus for optical interconnection between stacked IC chips.
In the optical transmission apparatus according to the sixth or seventh aspect, the base included in an optical transmission apparatus related to the third aspect and the base included in an optical transmission apparatus related to the fourth or fifth aspect are stacked in a manner such that the light emitting elements included in the optical transmission apparatus related to the third aspect respectively face the light receiving elements included in the optical transmission apparatus related to the fourth or fifth aspect. Therefore, an optical interconnection apparatus for optical interconnection between stacked IC chips can be easily realized.